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Solar panel controller size


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Hi All,

 

I’ve currently got a 100 watt solar panel with a 20amp controller . I’ve been lucky enough to be offered a 250 watt panel to replace my 100 watt. Question is what size controller do I need or is my 20amp enough? I can’t find any information is short in the subject hence turning to folks that might know.

 

help much appreciated ,

 

melanie 

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David thank you so much I’m so relieved to get an answer to this question that’s been with me for months. Honestly it’s made my day. I can now go forward with my plans to get more power coming into my boat. Thanks again ,

 

melanie

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I wonder if the controller can handle both panels? 

It seems a shame not to have both working if that's possible, and you might be able to get a mounting brackets pretty cheap, and borrow a drill and tap to make the holes? 

Its a job you can do yourself, and the folks on here will help if you have queries. 

 

I know my 50 amp controller can handle 750 watts of panels, so your 20 amp pone should be ok with 30 amps at least. But I dont know if it would be ok with 350 watts- hopefully someone will know, because you'd need a definite answer on that.

If the controller cant handle both panels, maybe you could pick up a cheap used controller on ebay?  

 

Sorry if I'm being a bit pushy, I think I'm solar mad 😀

 

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Hi Tony, thank you and please don’t apologise for being solar mad! I’ve simply don’t have the roof space to accommodate both and a good friend will be able to make use of it and add it to his collection 😆.

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You can only combine panels in series if they have the same or close Imp (max power current) or in parallel if they have the same or close Vmp (max power voltage). If they do not match then the combined set up will not harvest both panels and you could end up worse off as the lowest rated panel could pull the max power down to match it.

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3 minutes ago, PeterF said:

You can only combine panels in series if they have the same or close Imp (max power current) or in parallel if they have the same or close Vmp (max power voltage). If they do not match then the combined set up will not harvest both panels and you could end up worse off as the lowest rated panel could pull the max power down to match it.

The current rating is the current going into the batteries, not from the panels    Miss read your post

Edited by ditchcrawler
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It is definitely worth checking the specs  of your controller and the new panel before connecting them together. If it is just a cheap one it might not be designed to cope with a panel voltage over about 25v. If the controller is an Mppt from a decent brand its unlikely to be a problem. 

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Thanks Bilso I don’t think it’s a mppt controller as it doesn’t say it is. The spec label on the side is a bit blurred but here is a picture and one from the back of my new (secondhand) solar panel too. None of which means much to me. 

4C0B0A7A-FC72-4EFC-9872-7EF8EE0D5212.jpeg

A723FF2C-CFAD-48E0-B497-47329870541A.jpeg

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7 minutes ago, dontpanic said:

Thanks Bilso I don’t think it’s a mppt controller as it doesn’t say it is. The spec label on the side is a bit blurred but here is a picture and one from the back of my new (secondhand) solar panel too. None of which means much to me. 

4C0B0A7A-FC72-4EFC-9872-7EF8EE0D5212.jpeg

 

 

Could we have a focussed photo of the controller data label please? We need to read the first two lines in particular as I think your new panel voltage might be too high for it. 

 

 

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You will get ~30% more output if you buy a proper MPPT controller.

 

Test by Bimble Solar

 

 

PWM vs MPPT Charge Controller Test

We often get asked about the actual difference you get between an MPPT and a PWM controller so we setup a side by side test using our Yingli part used panels onto 2 separate 12V batteries, 1 with a PWM controller and one with our tracer MPPT. Panels were set-up side by side angled south.

With early March sun the MPPT was giving 3.7A into the batteries while the PWM gave 2.5A which was 32% lower than the MPPT.

In cloudy conditions the MPPT was giving 1A when the PWM was giving 0.8A (20% lower with PWM)

Both charged the batteries well, but 20%-32% more power was gained by using the MPPT.

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5 minutes ago, dontpanic said:

Very interesting thank you both. MPPT certainly sounds worth it. Now the question is which size? I have tried Victrons calculator but can’t find a controller for 250watt mono for 12v.

 

Your panel shows a short circuit current of 8.something volts and that is into a zero ohms resistance. You will get less than that from the panel so a 20 amp controller should  do fine, even 10 amps might do it but with 38 volts from the panes with the MPPT playing with the and and volts 20 amps will give a bit of headroom.

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1 minute ago, dontpanic said:

Very interesting thank you both. MPPT certainly sounds worth it. Now the question is which size? I have tried Victrons calculator but can’t find a controller for 250watt mono for 12v.

 

Personally I'd go for at least a 35 amp, but preferably a 50 amp, gives you room to 'grow the system' if you decide you need more.

 

A 20 amp would just about do the job but if on a cold February day you reached an excess of power it wouldn't matter as the controller would just use the most it could handle and the rest goes to waste.

 

Ensure that your controller is capable at operating at the panel voltage of your panels (my panels are 120 volt for example)

 

I'd strongly recommend Bimble - talk to them tell them what panel(s) you have and they will reccomend a suitable controller.

 

MPPT Charge Controllers (bimblesolar.com)

 

Expect to pay ~£100 for a decent one (scroll down the link to see the 20a, 30a, etc controllers)

 

You do not get quality, or MPPT, on a "£20 chinese controller, whatever it says on the label"

 

 

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1 hour ago, Alan de Enfield said:

You will get ~30% more output if you buy a proper MPPT controller.

 

Test by Bimble Solar

 

 

PWM vs MPPT Charge Controller Test

We often get asked about the actual difference you get between an MPPT and a PWM controller so we setup a side by side test using our Yingli part used panels onto 2 separate 12V batteries, 1 with a PWM controller and one with our tracer MPPT. Panels were set-up side by side angled south.

With early March sun the MPPT was giving 3.7A into the batteries while the PWM gave 2.5A which was 32% lower than the MPPT.

In cloudy conditions the MPPT was giving 1A when the PWM was giving 0.8A (20% lower with PWM)

Both charged the batteries well, but 20%-32% more power was gained by using the MPPT.

I think the solar panel voltage may have a bearing on this and how close it is the the battery voltage

1 minute ago, Alan de Enfield said:

 

 

 

You do not get quality, or MPPT, on a "£20 chinese controller, whatever it says on the label"

 

 

A lot of them are just PWM with MPPT written on them

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Just a word on the MPPTs- as a relative novice myself, I found the Victron much easier to program and to use than the Epever.

 

Victron even have an app that lets you manage the charging from your phone (when in bluetooth range). 

You can get a bluetooth add-on for some of the Epevers, but the app is not nearly as easy to use as the victron app.

 

But that said, the victrons do come at a higher price, and Epever are undoubtedly decent quality units. 

 

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32 minutes ago, Tony1 said:

But that said, the victrons do come at a higher price, and Epever are undoubtedly decent quality units. 

 

Given the only point of buying an MPPT controller is to increase the solar harvest, the £100+ might better be spent (if spent at all) on more panels.

 

(In principle that is. ISTR the OP saying there is no space for more.)

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25 minutes ago, MtB said:

 

Given the only point of buying an MPPT controller is to increase the solar harvest, the £100+ might better be spent (if spent at all) on more panels.

 

(In principle that is. ISTR the OP saying there is no space for more.)

 

Absolutely- more panels.

I probably went too far with it tbh. I'm not sure anyone really needs 1400watts of panels for most of the year.

In Nov- Feb solar is a bit rubbish no matter how many panels you have, and in the spring/summer 1400 watts is more than you need, even to heat the water as well.

I could easily have got 80cm wide panels and had a bit less output, and the roof would have been safer to walk on that it is now with my 1m wide panels.

Live and learn, I guess. 

 

 

Edited by Tony1
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As others have already said your existing controller is not really the right thing for the new panel. I like the basic Victron 20a mppt as a fit and forget for about £100 or pay about an extra £40 for the smart version if you want to be able to monitor it from your phone. If going cheaper the ep ever or renogy ones might be worth  a look.

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